I would like to have 'a legacy-defining task' expressed in other phrases.

The Walt Disney Company said Thursday that it had reached a deal to buy most of the assets of 21st Century Fox, the conglomerate controlled by Rupert Murdoch, in an all-stock transaction valued at roughly $52.4 billion.
To complete the integration, a legacy-defining task, Robert A. Iger, Disney’s chief executive, agreed to renew his contract for a fourth time, delaying retirement from July 2019 to the end of 2021._________________Hiromichi

I would like to have 'a legacy-defining task' expressed in other phrases.

The Walt Disney Company said Thursday that it had reached a deal to buy most of the assets of 21st Century Fox, the conglomerate controlled by Rupert Murdoch, in an all-stock transaction valued at roughly $52.4 billion.
To complete the integration, a legacy-defining task, Robert A. Iger, Disney’s chief executive, agreed to renew his contract for a fourth time, delaying retirement from July 2019 to the end of 2021.

I didn't answer this at first because I didn't understand it. Having read it again today, it might be that Robert Iger is delaying his retirement because integrating the two companies is difficult, and in fact, is the kind of difficult task that can define his legacy. Does that make sense?